ZapUnits — the easy way to convert units
Type a number, pick two units, read the answer. Then see the whole relationship on a graph, and keep a history of every conversion you have run.
Kilometers
42.195
Miles
26.219
- km
- °C
- GB
- psi
- acre
- lb
- mmHg
- kWh
- mi
- ha
- m/s
- °F
- ft
- gal
- bar
- N·m
…and 616 more, across 64 categories
Quick convert
All converters
Pick a category to convert between any two of its units.
Most searched conversions
Straight to the answer — each page includes the formula and a chart.
Every conversion, one keystroke away
632+ units across 64 categories — from centimetres and kilowatt-hours to bighas, centipoise and blood glucose. Search finds the unit before you finish typing it.
See the relationship, not just the number
Every conversion plots on an X/Y graph so you can read off any value at a glance — and see immediately why fuel economy and pace curve instead of running straight.
Your history, saved and chartable
Create a free account and every conversion you run is kept. Pull the list back up later, filter it, and plot your past conversions on the same chart.
Your conversions, kept and charted
Sign in and every conversion you run is saved automatically — no button to remember. Come back later, filter by category, and pick any entry to see it plotted.
Run the same conversion more than once and it becomes a series: input and result tracked over time, so you can watch a figure move across a project rather than recalculating it from scratch.
From the blog
Guides that explain the units, not just the arithmetic.
Earth Is Spinning Faster: The Shortest Days on Record
For most of history the Earth has been slowing down, and clocks added leap seconds to keep up. Since about 2020 it has been speeding up instead — fast enough that timekeepers feared the first negative leap second ever.
Ring Size Conversion: US, UK, EU and the Millimetres That Matter
Only one ring-size number is standardised: the inner circumference in millimetres. US numbers, UK letters and EU sizes are all conventions layered on top of it.
A4 vs US Letter: Paper Sizes Explained
Most of the world prints on A4; North America prints on Letter. They look interchangeable and are not, which is why a document shrinks to 94% when it crosses the Atlantic.